Alright it seems the glitch occurs only at random. Just search a new Free Roam until you get the glitch.
I recommend doing it at Fort Mercer. The glitch works with almost no downtime there. You get around 400xp/3sec.

Alright it seems the glitch occurs only at random. Just search a new Free Roam until you get the glitch.
I recommend doing it at Fort Mercer. The glitch works with almost no downtime there. You get around 400xp/3sec.

EDIT: Also set your aiming to expert for an extra 100XP each time.

Good tips dude. I was playing recently some free roam and coop but no go on the glitch. Was considering clearing game data and seeing if that has any effect on the glitch.